Detector apparatuses of the kind recited above often have a temperature-dependent dark current that causes noise. This dark current can be reduced by cooling.
DE 10 2009 036 066 A1 discloses an optoelectronic detector that comprises a cooling apparatus, namely a Peltier element, thermally conductively connected to the detector. To avoid the occurrence of condensed water on a surface of the optoelectronic detector, a sensor is provided in order to ascertain an instantaneous value with regard to the ambient relative humidity and ambient dew point temperature. The sensor is connected to a control unit that controls the cooling apparatus as a function of the value. This optoelectronic detector has the advantage that cooling is not entirely dispensed with. It has the disadvantage, however, that the actual cooling output is limited to a small amount, namely the amount at which no condensation occurs. The result of this is that detector noise is only insufficiently avoided.
The same document mentions another detector apparatus in which the detector is encapsulated along with the cooling apparatus, typically a Peltier element, in an airtight housing that is filled with a dry gas or evacuated. With this apparatus, the waste heat of the cooling apparatus can be delivered to a cooling element that is thermally conductively connected to the cooling apparatus and/or can be used to heat other components, for example an entrance window of the housing. This detector is to be considered disadvantageous, however, since the airtight encapsulation is complex.
It has in fact been found in practical use that this detector apparatus has even further disadvantages. In particular, cooling is often not very effective. Cooling moreover turns out to be particular difficult if the detector must be at a different electrical potential level than the housing. In this case the Peltier element cannot easily be arranged between the housing and detector. A potential difference of this kind is usually necessary when acceleration of photoelectrons is to occur inside the detector.
U.S. Pat. No. 5,508,470, U.S. Pat. No. 5,596,228, or U.S. Pat. No. 4,833,889, for example, disclose detector apparatuses in which an active cooling apparatus is provided respectively on that side of a light sensor which faces away from a light incidence side. These detector apparatuses have the disadvantage that a large portion of the cooling output is unused and lost.
WO 99/59186 also discloses a detector apparatus having a cooling system, namely a detector apparatus having a photomultiplier cooled by means of a Peltier element.